Exposure control apparatus



Aug. 19, 1941.

C. M. TUTTLE ETAL EXPOSURE CONTROL APPARATUS Filed March 1 5, 1940 FIG.

I CLIFTONM.TUTTLE C? ALLAN MKOERNER INVENTORS /EaLzuZZ Patented Aug. 19, 1941 sxrosuas con'rnor. APPARATUS Clifton M. Tuttle )nd Allan M. Koerner, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application March 15, 1940, Serial No. 324,231

3 Claims.

circumstances a measure of the time of exposure fails. as a measure of total exposure.

It is an object of this invention to minimize the difliculty arising from intensity variation during an exposure period by providing apparatus for regulating the exposure period substanl5 tially in accordance with the average intensity- Another object of the invention is to provide apparatus which controls the length of an exposure in accordance with the summation of a tensity for each of said periods whereby the length of the exposure is determined by the number of said periods necessary for obtaining the quantum of light required for correct exposure.

Other objects and advantages of the invention Fig. 1 is a diagrammatic perspective view of an arrangement embodying the invention as applied to a process camera; and

Fig. 2 is a front elevation of an indexing means shown in Fig. 1.

According to the invention, at periodic interv vals during an exposure to be regulated, a light sensitive means samples the illumination or other factor bearing a known relation to the expomng light and during each such interval the has been found that a large number of uniformly 4 spaced samples each accompanied by the required correction is suillciently representative of the exposure history to give satisfactory results.

In the drawing one form of the invention is 3 shown as applied to a copying camera ll such -50 asisnormallyusedinprocess work. The camera llhasthe usuallenstubellcoveredbyacap l2 whichisremovableformakinganexposure. A suitable copy board I! mworted'on a base in any well known mannerto hold material to be copied and may be illuminated by lamps II. The lamps ll, here shown as the arc type, are adapted to be suitably energized as by being connected in parallel across leads II which may be energized by any suitable source not shown. If desired, the lamps I! may each be provided with circuit making and breaking means IS.

The lens cap I2 is carried on one end of an arm 20 pivoted at 2| and having its other end connected to the armature 22 of a solenoid 23 which is adapted to be connected to the line it by a switch 24 and through leads 25. When the switch 24 is closed to energize the solenoid 23,

the arm 2| is moved against the bias of a spring 26 to move the cap l2 from in front of the lens tube It thereby starting an exposure.

For determining the length of the exposure the I h following arrangement is employed. A toothed plurality of uniform periods multiplied by the in- 2n disc 21 mounted for rotation about an axle 2' is-adapted to be indexed in a clockwise direction by a pawl 29 carried by an oscillatable arm ill which is pivoted on the axle 2|. The arm I. is periodically rocked as by an eccentric roller ll secured to a shaft 32 which is rotated at a uniform speed by a motor a driven through Bears 34 and It. The constant speed driven motor Il may be an electric synchronous motor connected tothelines l8 throughthe switch 2|sothatthe rocking movement of the arm II is commenced when the switch 24 is moved to closed position to start the exposure. If the amplitude of the rocking movement of the arm II was constant. the pawl 20 would index the disc 21 through the same angle for every oscillation and a predetermined angular movement of the disc 21 would always correspond to a fixed time interval. Thus,

.ifacertainpointsuchasseroonthediscfl isplaced oppositeanindexmarkll when the exposure is proportionally lengthened or shortswitch 24 is closed. apredetermined time interval willhave elapsedwhenthepartofthedisc 21 carrying the numeral 8 comes opposite the index ll and-if somemeansisprovided.suchas apinl'Ltoopentheswitchflwhenthedisc has moved this amount. the solenoid 22 willbe de-energized and the-spring 2i willforcethecap back to the position shown in Fig. 1 at which theexposureisterminated- I In making relatively long exposures, the illuminationofthe subjectcarriedbytheboard Ills likelytovaryandaflxedtimeofexpcmrewill not necessarily result a correct exposure. Therefore, it is desirable to shorten or lengthen theexposureintervaltocompensateforanymch II by telescoping members lland ll isadapted 68 varlatlonsintheillumination. 'lhismaybedme by making the indexing movement of the disc 21 by the pawl 29 depend upon the illumination and in the embodiment of the invention shown in the drawing, this is accomplished by providing a meter 38 with a pointer 35 movable in the path of a notched scimitar blade 40 provided at the end of the rocking arm 30. The meter 38 is energized in accordance with the illumination the copy board l3 by means of a photoelectric cell ll acting through an amplifier 12. It will thus be seen that. depending upon the position of the meter pointer 39, the extent of the rocking movement of the arm 30 is limited and the arrangement is such that an increase or decrease of the illumination from what may be considered normal results in a corresponding increase or decrease, respectively, of the rocking movement of the arm 30 and, therefore, in the angle through which the disc 21 is indexed.

With the arrangement above described, if it is found that an angular movement of the disc 21 from zero to 6 gives correct exposure for normal illuminatiom then, if during the exposure the illumination varies, the corresponding variation introduced into the amplitude of the oscillating arm 30 by the ,meter pointer 39 will result in a corresponding change in the time interval to give a proper exposure. It will be understood that the speed of rotation of the eccentric disc 3| will be high enough to insure that a relatively large number of oscillations of the arm 30 will take place during a single exposure to the end that enough samples of the illumination will be taken to make it reasonably certain that any variations in illumination will have been followed with suiilcient accuracy to give satisfactory results.

While the specific embodiment of the invention has been described in detail to make it clear to those skilled in the art, many modifications will readily suggest themselves and all such modifications are intended to be included in the appended claims.

What we claim and desire to be securedby Letters Patent of the United States is: V

1, In photographic copying apparatus requiring relatively long exposures, means for illuminating the subject being copied, means for initiating an exposure, light sensitive means for providing an electric current proportional to and variable with the illumination of the subject, a ratchet disc, an oscillatable arm, a pawl carried by said arm for indexing said d sc in accordance with the amplitude of oscillation of said arm, means for oscillating said arm at a uniform relatively high frequency, means for simultaneously actuating said exposure initiating means and said arm oscillating means, means controlled by said current for governing individually the amplitude of each oscillation, whereby the time required for indexing said disc a predetermined amount will depend substantially upon the average intensity of the illumination 0! the subject, exposure terminating means, and means responsive to a predetermined amount of indexing of said disc for actuating the exposure terminating means.

2. Means for providing a time interval corresponding to the average intensity of illumination comprising means movable through a path of predetermined length for providing the time interval, a rocker arm for indexing the movable means along said path, means for rocking said arm periodically, and means for governing the extent of each such rocking movement in accordance with the intensity of the illumination existing during the period between each rocking movement.

3. In apparatus for regulating the length or a photographic exposure of relatively long duration the combination of means for translating variations of light intensity into distance increments comprising means for producing periodic increments of variable size, means for controlling the size of each of said increments in accordance with the intensity of the exposure taking place, and means for terminating the exposure when said increments total a predetermined distance.

CLIFION M. TUTI'LEL ALLAN M. KOERNER. 

